Notice: Undefined offset: 27 Why these error generated in PHP? - php

Question

I used below code but that gives me an Error like "Notice : Undefined offset: 27" . Why these error generated or what these error means ? please any one help me.
//Code ... final_display2 is found some array.
for($p=0; $p<sizeof($final_display2); $p=$p+2){
$b = $p+1;
$len1 = strlen($final_display2[$p])+strlen($final_display2[$b]); //these line gives error 116
if($len1 < 3200){
array_push($final_display,$final_display2[$p].$final_display2[$b]); //and these one also 118 }else{
array_push($final_display,$final_display2[$p]);
array_push($final_display,$final_display2[$b]);
}
}
ERROR!!

Answer 1

Your error occurs when $p==sizeof($final_display2)-1, so $b==sizeof($final_display2), which will result in a Undefined Offset.
ie. if sizeof($final_display2)==27, when $p==26, then $b==27 and $final_display2[$b]/$final_display2[27] does not exist.
Try using if(isset($final_display2[$b])) ->
for($p=0; $p<sizeof($final_display2); $p=$p+2){
$b = $p+1;
if(isset($final_display2[$b])){ //only run if $final_display2[$b] exists
$len1 = strlen($final_display2[$p])+strlen($final_display2[$b]); //these line gives error 116
if($len1 < 3200){
array_push($final_display,$final_display2[$p].$final_display2[$b]); //and these one also 118 }else{
array_push($final_display,$final_display2[$p]);
array_push($final_display,$final_display2[$b]);
}
}
}

Answer 2

Just use $p instead of $b since your looping trough all items in $final_display2, but your adding 1 to $b it's an offset! (Also change in your for loop this $p=$p+2 to $p++)
Little example:
You have 5 items in $final_display2 so the loop is like this:
for($p=0; $p<5; $p++)
//So if your at the last element ($p = 4) but your adding 1 to $b and use it you have a offset
Edit:
I think your looking for something like this:
foreach($final_display2 as $k => $v) {
if( isset($final_display2[$k+1]) ) {
if($k == 0 || $k % 2 == 0) {
$len1 = strlen($final_display2[$k])+strlen($final_display2[$k+1]);
if($len1 < 3200){
array_push($final_display,$final_display2[$k].$final_display2[$k+1]);
array_push($final_display,$final_display2[$k]);
array_push($final_display,$final_display2[$k+1]);
}
}
}